Many physical systems operate in cooperation with an adjunct system. The purpose of the physical system is usually the performance of one or more functions, and the purpose of the adjunct system is to help the physical system perform its functions better. Usually, the adjunct system helps the physical system perform its functions more efficiently or perhaps faster, but it may also prevent the physical system from self-destructing, or help the physical system self-destruct with minimum losses, or simply warn of a condition of the physical system. Two types of adjunct systems are monitoring systems and control systems, both of which are usually implemented electronically at least in part. Both of these adjunct systems may be required to make decisions which improve the physical system's performance. For example, a monitoring system may be required to decide when to indicate the presence of a condition in the physical system, such as sounding an alarm when an electric motor is about to fail. More sophisticated monitoring systems may also decide what physical attributes of the physical system they will monitor and when.
A control system will typically include a system for monitoring the physical system, making decisions, and issuing commands based on those decisions to change the physical system. In such adjunct system, it has been suggested by the current inventors that decision trees might be used to make decisions in the process of monitoring and/or controlling the physical system, but it was recognized that known techniques for implementing decision trees did not work better than conventional control systems. ("A Variable-Speed Induction Motor Drive Using Expert System Technology", J. Douglas Birdwell, Roger D. Horn, et al., European Power Electronics Conference 1991 Proceedings, Firenze, Italy). The system described in the aforementioned paper would operate to control a linear system, which rarely occurs in the real world, but it would not successfully control or monitor non-linear systems that are typically encountered, such as a motor.